What are ducts installed below ground level referred to as?

Ducts installed below ground level are commonly referred to as "Underground Ducts." This terminology is widely accepted in the field of mechanical systems and HVAC design. The use of underground ducts is significant in various applications, including the transportation of air or other gases for ventilation and climate control, especially in commercial buildings.

The term "underground" accurately represents the location of these ducts, clearly indicating that they are situated below the surface. This location can help optimize space above ground for other construction needs while ensuring that the HVAC system operates effectively, protected from the elements.

In some contexts, other terms like "buried ducts" might be used interchangeably, but "underground ducts" is the more standardized term in professional practice and documentation. Understanding the nomenclature around ductwork helps inspectors and engineers communicate effectively about systems and ensures compliance with building codes and standards.